The present invention relates to a new and improved method for forming a rotor and more specifically to a method of forming a rotor having a circular hub with a plurality of blades projecting from the hub.
The concept of forming the blades and hub of a rotor for a gas turbine engine of different materials is disclosed in U.S. Pat. No. 4,051,585. In practicing the method disclosed in this patent, a plurality of turbine blades are placed in a circular array. Preformed discs, having grooves in their radially outer edge portions, are pressed against the roots of the blades. The discs are diffusion bonded together. The discs are formed of a wrought superalloy having a fine grain microstructure.
U.S. Pat. No. 3,905,723 discloses the concept of making a gas turbine rotor by providing an annular array of preformed blades. Two preformed discs of carbide or silicon nitride molding powder are pressed together to form a hub which is connected with the blades.
The concept of arranging blades in a circular array and hot isostatically pressing powdered ceramic or superalloy materials around the blades is disclosed in U.S. Pat. Nos. 4,097,276 and 3,940,268. These patents contemplate that the hot isostatic pressing process will occur with the blades extending into the powder being bonded.
The hubs of the rotors formed in accordance with the foregoing patents will have substantially the same metallurgical characteristics throughout the radial extent of the hubs. However, the concept of forming a rotor from powdered metal and varying the metallurgical characteristics of the rotor by using powdered metal having different characteristics is disclosed in U.S. Pat. No. 4,329,175.
The concept of forming the rim portion of a disc with a coarse grain and forming the central portion of the disc with a fine grain is disclosed in NASA Report No. CR-165224 by Kortovich and Marder and entitled "Development of Materials and Process Technology for Dual Alloy Disks". The report indicates that the rim portion of a disc is formed from powdered metal by hot isostatic pressing of the powdered metal. The rim portion of the disc is then filled with powdered metal and is enclosed in a container. The enclosed rim portion and powdered metal are then subjected to a hot isostatic pressing operation.